PL189780B1 - Two-pole plate of a separator for stack of fuel cells, method for manufacture of two-pole separator plate for stack of fuel cells and stack of fuel cells - Google Patents

Abstract

A gas impervious bi-polar separator plate for a proton exchange membrane fuel cell having at least one electronically conductive material in an amount in a range of about 50% to about 95% by weight of the separator plate, at least one resin in an amount of at least about 5% by weight of the separator plate, and at least one hydrophilic agent, where the electronically conductive material, the resin, and the hydrophilic agent are substantially uniformly dispersed throughout the separator plate.

Description

The present invention relates to a bipolar separator plate for a fuel cell stack, a method for producing a bipolar separator plate for a fuel cell stack, and a fuel cell stack.

The present invention relates to a bipolar separator plate for use in a fuel cell stack with proton exchange membranes.

There are known fuel cells in which the separator plate is hydrophilic and has a controlled porosity that facilitates internal wetting of the fuel cell as well as removal of water formed in the fuel cell, while allowing the temperature of the fuel cell stack to be controlled.

Known electrical fuel cell systems consist of a stacked plurality of individual cells separated by bipolar electronically conductive separator plates. The individual cells are stacked on top of each other and connected in a one-piece system to obtain the desired output energy of the fuel cell system. Each individual cell generally includes electrodes, anode and cathode, an electrolyte, and a fuel and an oxidizing gas source. Both the fuel and the oxidizing gases are introduced through a distribution conduit system located either inside or outside the fuel cell stack, into the respective reaction chambers between the separator plate and the electrolyte.

Fuel cells are known and are suitable for use in a variety of applications including power generation, driving cars, and others where environmental pollution must be avoided. These include fuel cells with liquid carbonate, solid oxide, phosphoric acid and a proton exchange membrane. One of the problems with the successful operation of any type of fuel cell is controlling the temperature of the fuel cell and removing products generated by electrochemical reactions from within the fuel cell.

Usable commercial fuel cell stacks may contain up to about 600 individual fuel cells, each of which has a surface area of 1.08 m ^2. In stacking such individual cells, the separator plates separate the individual cells, and fuel and oxidant are introduced between the set of separator plates; the fuel is introduced between one surface of the separator plate and the anode side of the electrolyte, and the oxidant is introduced between the other surface of the separator plate and the cathode side of the second electrolyte. Cell stacks containing 600 cells can be as high as 6 m, creating serious problems in maintaining the integrity of the cells during annealing and operation of the fuel cell stack due to temperature gradients in the cell assembly and the operating conditions of the cells, differential thermal expansion and the necessary strength of the materials ·; required for different components, small tolerances and very difficult engineering problems. Accordingly, control

Cell temperature is very important and, if not implemented with a minimum temperature gradient, the current density will not be kept uniform and cell degradation will occur.

In a proton exchange membrane (PEM) fuel cell, the electrolyte is an organic polymer in the form of a proton permeable membrane, such as a perfluorosulfonic acid polymer. This type of fuel cell works best when the electrolyte membrane is wetted with water because the dry membrane does not work efficiently. During cell operation, water is pulled across the membrane from the anode side to the cathode side with protons passing through the membrane. This causes the anode side of the membrane to dry out and also causes a water film to form on the cathode side of the membrane. The cathode surface is further wetted by the water produced by the electrochemical reaction. Thus, it is critical to the operation of the PEM fuel cell that the reaction water is continuously removed from the cathode side of the membrane while keeping the anode side of the membrane wetted to facilitate electrochemical reaction and maintain the membrane conductivity.

Water management in a proton exchange membrane fuel cell is covered by several US patents. U.S. Patent No. 4,769,297 teaches the use of a solid polymer fuel cell in which water is supplied with anode gas to the anode side of the diaphragm. A certain proportion of the water migrates through the stack from cell to cell, the migration of water being the result of dragging water from the anode through the membrane to the cathode and by using a hydrophilic, porous separator plate disposed between adjacent cells. Water is forced through the porous separator plate by the pressure differential of the reaction components, held between the cathode and the anode. The anode support plates have a large surface area from which water evaporates to provide cooling. It is suggested that the separator plate be made of graphite. /

U.S. Patent No. 4,826,741 describes a fuel cell system using a porous graphite anode plate. Water is supplied to the porous plate and the anodic reaction gas is wetted by evaporation from the plate surface. The proton exchange membrane is wetted by contact with the moist, porous anode plate. A non-porous and gas-tight separator plate adjacent to the cathode plate is used to prevent gas from permeating from the anode to the cathode. See also U.S. Patent Nos. 4,826,741, No. 4,826,742, No. 5,503,944 and PCT Patent Application No. WO 94/15377.

Bipolar separator plates for use in proton exchange membrane cells constructed of graphite or resin bonded graphite carbon and having gas flow channels are disclosed in US Patent No. 4,175,165. Also described is the treatment of bipolar separator plates by coating the surfaces with a wetting agent such as colloidal silica to make the surfaces hydrophilic. In this way, the water produced in the fuel cell is drawn from the electrodes and remains available. However, coating the surface with a wetting agent undesirably increases the electrical resistance across the plate, resulting in a reduction in conductivity. US Patent No. 3,634,569 describes a method of making high-density graphite plates from a mixture of graphite powder and a thermostatic resin for use in an acid fuel cell. The method uses a mixture (given in wt.%) Of 5% to 25% thermosetting phenolic resin tackifier and 75% to 95% powdered graphite graded. Graphite-resin bipolar plates are also shown in U.S. Patent No. 4,339,322 (bipolar plate constructed of molten thermoplastic fluoropolymer, graphite and carbon fibers), U.S. Patent No. 4,738,872 (separator plate containing 50% by weight of graphite and 50% by weight of thermosetting phenolic resin) ), U.S. Patent No. 5,108,849 (serpentine flow plates in a fuel cell separator plate, constructed of non-porous graphite or other corrosion-resistant metal powders and a thermoplastic resin such as polyvinylidene fluoride in the proportion of 10-30% by weight of resin

189,780 and 70-90% by weight of graphite powder), U.S. Patent No. 4,670,300 (fuel cell plate containing 29% to 80% graphite with a complement of cellulose fibers or cellulose fibers and a thermosetting resin in equal proportions), U.S. Patent No. 4,592,968 (separator plate containing graphite, coke and carbonized thermosetting phenolic resin, which are then graphitized at 2650 ° C), U.S. Patent No. 4,737,421 (carbon or graphite fuel cell plate ranging from 5% to 45%, thermosetting resin ranging from 40% to 80%, padded with cellulose fibers), U.S. Patent No. 4,627,944 (carbon or graphite fuel cell plate, thermosetting resin and cellulose fibers), U.S. Patent No. 4,652,502 (fuel cell plate made in 50 % graphite and 50% thermosetting resin), U.S. Patent No. 4,301,222 (separating plate ator made of a mixture of 40% to 65% graphite and 35% to 55% resin) and U.S. Patent No. 4,360,485 (a separator plate made of a mixture of 45% to 65% graphite and 35% to 55% resin.

US Patent No. 4,175,165 teaches the use of various wetting agents such as ultra-high surface area colloidal silica or aluminum solutions or aluminum silica compounds that are deposited on the surface of the described separator plate. However, aluminum and silica, as well as other wetting agents, are generally electrical insulators. Thus, the application of a wetting agent to the surface of the separator plate causes the surface to become hydrophilic, but also increases the surface contact resistance of the plates, thereby increasing the internal resistance of the cells which, in turn, reduces the power of the cell.

Patent description AT 389 020 describes a hydrogen-oxygen fuel cell comprising a membrane and separator plates. In order to reduce the dehydration of the cell membrane, it is suggested either to make porous membranes and separator plates (micropores 0.001 to 1 µm) or to add a microporous hydrophilic agent such as kaolin or micro asbestos with sizes from 0.001 to 1 µm. The pores are filled with water in use, and the capillary forces are sufficient to make the separator plate gas impermeable.

The bipolar separator plate used in fuel cells with a proton exchange membrane has numerous features which are important from a manufacturing point of view as well as handling and which are not solved by the prior art. This includes the plate's water permeability as a function of the plate's electronic conductivity, the plate's fracture strength, the plate's functionality in terms of maintaining its ability to absorb water, and the plate's ability to undergo freezing-to-defrost thermal cycles such as may occur when using a fuel cell in a car. . Additionally, it should be possible to manufacture a separator plate from low-cost starting materials that can be easily formed into any plate configuration, preferably using a one-step casting process, that resists corrosion in low temperature fuel cells and that does not require further processing such as high temperature machining. and use a production method in which the water absorption and porosity of the board can be controlled.

According to the invention, a separator plate for a proton exchange membrane fuel cell stack comprising at least one electronically conductive material, at least one resin and at least one hydrophilic agent attracting water to the separator plate of a proton exchange membrane fuel cell stack is characterized in that the at least one electronically conductive material is a carbon containing material and the electronically conductive material is present in an amount from about 50% to about 95% by weight of the separator plate, at least one resin is a phenolic resin in an amount of at least about 5% by weight of the separator plate, and hydrophilic is silica in an amount of from 0.01% to 5% by weight of the separator plate, and the separator plate comprises carbon fibers in a maximum amount of up to 45% by weight of the separator plate, at least one electronically conductive material, at least one resin, at least one hydrophilic agent and i the carbon fibers are substantially evenly distributed.

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Preferably, the resin in the separator plate is hydrophilic. The hydrophilic agent is a wetting agent. The wetting agent comprises a mixture of silica and metal oxides selected from the group consisting of Ti, Al.

The at least one resin is selected from the group consisting of thermosetting resins, thermoplastic resins, and mixtures thereof.

The at least one carbon-containing electronically conductive material is selected from the group consisting of graphite, carbon black, carbon fibers, and mixtures thereof.

Preferably, the separator plate is porous. The separator plate porosity is less than 25% by volume of the plate. The pores have an average diameter ranging from 0.25 microns to 2.0 microns. The bubble pressure of the plate is greater than 34.5 kPa.

The specific electrical conductivity of the separator plate is at least 5 S / cm.

The separator plate preferably comprises 70% to 90% by weight of the carbon-containing electronically conductive material, 8% to 15% by weight of thermosetting phenolic resin, up to 10% by weight of carbon fibers, and 0.01% to 5.0% by weight of silica.

Between the surface of the separator plate facing the anode and its surface facing the cathode there are elements for circulation of water

According to the invention, the method of producing a bipolar separator plate for a fuel cell stack consists in mixing at least one electronically conductive material, at least one resin, at least one hydrophilic agent selected for the fuel cell with a proton exchange membrane, and then shaping plates of the required shape.

The method is characterized in that the at least one electronically conductive material is a carbon containing material in an amount of 50% to 95% by weight of the mixture, a phenolic resin in an amount of at least 5% by weight of the mixture is used as the at least one resin, and a hydrophilic agent is used as silica in an amount of 0.01 to 5% by weight of the mixture, and carbon fibers in a maximum amount of up to 45% by weight are added, and these components of the mixture are mixed until a homogeneous mixture is obtained, and then a separator plate is shaped at the temperature of 121 ° C to 260 ° C and pressures ranging from 3447 kPa to 27579 kPa.

The at least one resin is a hydrophilic resin.

A wetting agent is used as the hydrophilic agent. Preferably, a hydrophilic agent is used in the form of a mixture of silica and a metal oxide selected from the group consisting of Ti, Al.

A phenolic resin is used selected from the group consisting of thermosetting resins, thermoplastic resins, and mixtures thereof.

A carbon-containing material selected from the group consisting of graphite, carbon black, carbon fibers, and mixtures thereof is used.

According to the invention, the fuel cell stack comprises a plurality of individual fuel cells, each comprising an anode, a cathode, an ion exchange membrane disposed between the anode and cathode, and a separator plate having an anode-facing surface and a cathode-facing surface, the plate being The separator is located between the anode of one fuel cell and the cathode of an adjacent fuel cell, and comprises at least one electronically conductive material, at least one resin, and at least one hydrophilic agent.

The cell stack according to the invention is characterized in that the separator plate comprises, uniformly distributed therein, at least one electronically conductive carbon-containing material in an amount ranging from 50% to 95% by weight of the separator plate, at least one phenolic resin in an amount of at least 5% of the separator plate, a silica hydrophilic agent in an amount of 0.01% to 5% by weight of the separator plate, and contains carbon fibers up to 45% by weight of the separator plate, and each of the ion exchange membranes and separator plates extends up to the edge of the fuel cell stack, the separator plate having flat peripheral sealing structures protruding from each surface of the separator plate into contact with the ion exchange membranes around their entirety

189 780 and forming an edge seal, and the ion exchange membrane and the separator plate have a plurality of fuel and oxidant distribution openings opposite each other, the separator plate distribution openings being surrounded by flat sealing structures extending from the surface of the separator plate into contact with each other. an ion exchange membrane and forming distribution channels for gaseous fuel and oxidant, extending through the stack of cells, and in flat sealing structures there are gas fuel flow conduits formed between one set of distribution channels and anode chambers formed between the anodes and the surfaces of the separator plates facing the anodes, and oxidant gas flow conduits are formed between the second set of distribution channels and the cathode chambers formed between the cathodes and the cathode-facing surfaces of the separator plates.

The separator plate comprises at least one hydrophilic resin.

The separator plate's hydrophilic factor is wetting. The separator plate hydrophilic wetting agent comprises a mixture of silica and metal oxides selected from the group consisting of Ti, Al.

The phenolic resin of the separator plate is selected from thermosetting resin, thermoplastic resin, and mixtures thereof.

The at least one carbon-containing electronically conducting material of the separator plate is selected from the group consisting of graphite, carbon black, carbon fibers, and mixtures thereof.

The separator plate contains pores. The separator plate porosity is less than 25% by volume of the plate. The pores of the separator plate have an average diameter ranging from 0.25 microns to 2.0 microns. The separator plate has a bubble pressure greater than 34.5 kPa.

The separator plate has a specific electrical conductivity of at least 5 S / cm.

The gas flow lines are formed in a central area of the separator plate.

The fuel cell stack includes water distribution holes for circulation and removal of water from the fuel cell stack.

The present invention provides a bipolar separator plate suitable for use in a proton exchange membrane fuel cell, which is relatively inexpensive to produce, yet has improved water removal and internal wetting properties for a proton exchange membrane fuel cell. The separator plate for a proton exchange membrane fuel cell of the invention has an advantageous crush strength greater than about 1380 kPa.

The bipolar separator plate of the invention is suitable for use in a fully internally distributed fuel cell stack.

The invention is illustrated in the drawing in which Fig. 1a shows a side view of a PEM fuel cell stack with one-piece separator plates according to one embodiment of the present invention; Fig. 1b is a side view of a PEM fuel cell stack with two-piece separator plates according to a second embodiment of the present invention; Fig. 2 is a diagram showing the conductivity of the separator plate versus the percentage of silica as wetting agent in the separator plate; Fig. 3 is a diagram of the dependence of the amount of water absorbed by the separator plate on the percentage of silica in the separator plate, and Fig. 4 is a diagram of a fuel cell stack with internal fuel distribution.

Figures 1a and 1b show a fuel cell stack 15 having a plurality of fuel cells 20, each fuel cell including a proton exchange membrane 25, an anode 30 on one side, and a cathode 35 on the other side. Between the anode 30 and the proton exchange membrane 26 there is a layer of anode catalyst 31, and between the cathode 35 and the proton exchange membrane 25 is a layer of the corresponding cathode catalyst 36. The anode 30 of one cell is separated from the cathode 35 of an adjacent cell by a bipolar separator plate 39.

According to the first embodiment of the present invention, as shown in Fig. 1a, the separator plate 39 of the present invention is in one piece and has a surface of 40.

189 780 facing the cathode 35 and the surface 45 facing the anode 30. A plurality of cathode channels 41 for the flow of oxidizing gas are formed on the surface 40 facing the cathode 35, extending therein to allow contact between the oxidant in the cathode channels 41 and cathode 35. Likewise, in surface 45 facing the anode 30 are respective fuel gas flow anode channels 46 formed therein to allow contact between the fuel gas and the anode 30.

According to another embodiment of the present invention, as shown in Fig. 1b, the separator plate 39 is constructed of two plates: a cathode side cathode plate 39a and an anode side anode plate 39b. In order to provide water cooling of the stack, the surfaces of the cathode plate 39a on the cathode side 35 and the anode plate 39b on the anode side 30 are provided with a plurality of intermediate channels 34 for cooling water flow.

The fuel cell stack also includes a cathode end plate 50 of the separator and an anode end plate 60 of the separator. The cathode 50 and anode 60 end plates are impervious to water or are otherwise sealed to prevent leakage. Suitable tensioning mechanisms and seals (not shown) are provided to connect the stack members to one another.

For this reason, the separator plate of the present invention must be strong enough that it does not collapse under the action of the forces applied to it during assembly of the fuel cell stack. The separator plate crushing strength must be greater than 1380 kPa. The separator plate produced according to Example 5 has a crush strength greater than 14,490 kPa. In addition to the crush strength, the separator plate of the present invention must have some degree of flexibility to conform to other components of the fuel cell assembly. According to a particularly preferred embodiment of the present invention, the separator plate has a minimum flexibility of 3.5% or about 0.036 cm. per centimeter long without breaking.

The fuel cell gas-impermeable bipolar separator plate 39 in the fuel cell stack according to the present invention with an attached proton exchange membrane 25 has a body containing at least one electronically conductive material, at least one resin, and at least one hydrophilic agent, the electronically conductive material, a resin. and the hydrophilic agent are substantially uniformly distributed in the body of the separator plate 39. The separator plate 39 of the present invention eliminates the need for external wetting of the fuel cells with the proton exchange membrane 25 and facilitates the regulation of heat and removal of water formed in the fuel cell system. The preferred composition of the bipolar separator plate 39 of the present invention comprises a mixture of graphite and resin which, when extruded under average pressure and temperature conditions, produces a conductive, lightweight bipolar plate suitable for use in low temperature electrochemical systems such as proton exchange membrane fuel cells.

The separator plate 39 preferably includes tunnels for the flow of reaction fluids for a given electrochemical system. The separator plate 39 can be manufactured with a different conductivity according to a given electrochemical system. The separator plate 39 can be manufactured with a variety of porosities to properly manage the water in a given electrochemical system. In addition, the separator plate 39 can be manufactured with different hydrophilicity to suitably manage heat and water in a given electrochemical system.

According to the invention, the bipolar separator plate 39 comprises at least one electronically conductive material in an amount from 50% to 95% by weight of the plate, at least one resin in an amount of at least 5% by weight of the plate, and at least one hydrophilic agent. Separator plate 9 also includes carbon fibers that are uniformly distributed throughout the plate in an amount up to about 20% by weight of the plate, but most preferably less than 10% by weight of the separator plate. Although carbon fibers are expensive, their use provides adequate porosity and structural reinforcement without degrading conductivity as much as using an adequate amount of wetting agent.

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The separator plate 39 according to a particularly preferred embodiment of the present invention is made of a mixture of about 50 to 95 wt% graphite material, especially graphite, about 5 to about 30 wt% thermosetting resin, 0 to about 45 wt% carbon fibers, 0 up to about 25 weight percent silica. The mixture is then extruded at an elevated temperature ranging from about 121 ° C to about 260 ° C and a pressure ranging from about 3447 kPa to about 27579 kPa. The conductivity of the thus extruded separator plate 39 is at least about 5 S / cm, which represents nominally the minimum conductivity required for use in a proton exchange membrane fuel cell. The porosity of the extruded material is approximately 25% by volume. The bubble pressure of the extrudate, which increases as the volume of the voids in the separator plate 39 decreases, is at least about 34.5 kPa.

Fuel cell 15 with proton exchange membrane 25 made of solid polymer electrolyte works best when such proton exchange membrane 25 is kept wetted with water. When the fuel cell 15 is operated with the proton exchange membrane 25, water is pulled through the proton exchange membrane 25 from the anode side to the cathode side with protons moving through the proton exchange membrane 25. This phenomenon causes the anode side of the proton exchange membrane 25 to dry out while producing water droplets. on the surface of the proton exchange membrane 25 facing the cathode 35. The surface 36 facing the cathode 35 is further wetted by the water generated by the electrochemical reaction which appears on the surface 36 facing the cathode 35. If not properly managed, the water on the surface 36 facing the cathode 35, particularly in the form of droplets, can clog the oxidant channels, thereby blocking access of the oxidizing gas to the catalyst and reducing the electrochemical reaction.

Accordingly, it is essential that water is supplied to the anode side of the proton exchanging membrane 25 in fuel cell 15 to prevent it from drying out and that water is continuously removed from the cathode side to prevent water droplets from forming on the membrane surface. The separator plate 15 of the present invention is sufficiently water-absorbent not only to prevent water from accumulating on the cathode side, but also to support water distribution therethrough. Due to the presence of water in the separator plate 39, the possibility of mixing the reaction gases in the separator plate 39 is greatly reduced. Accordingly, the bipolar separator plate 39 of the present invention includes at least one hydrophilic agent substantially uniformly distributed throughout the plate, suitable for use in a proton exchange membrane fuel cell to attract water to the separator plate 39.

According to one preferred embodiment of the present invention, the at least one resin in the separator plate is wetland. According to a particularly preferred embodiment of the present invention, the hydrophyte resin is a thermosetting phenol-formaldehyde resin.

According to another embodiment of the present invention, the at least one hydrophilic agent is a wetting agent, preferably selected from the group consisting of Ti, Al, Si oxides and mixtures thereof. As a result of the distribution of the hydrophilic medium in the separator plate, the separator plate of the present invention has sufficient water permeability to remove at least 5.5 cm ^{3 of} water per minute at a current density of 1.1 A / cm ² at a pressure difference of less than about 69 kPa.

One application of a proton exchange membrane fuel cell is to generate energy in cars. In this application, the fuel cell is exposed to large variations in temperature and may undergo numerous freeze / thaw cycles during operation. It can be expected that the holding of water inside the separator plate due to the absorption of water by the plate due to the distribution of the water-repellent agent in the plate will cause the plate to crack upon changing the temperature from freeze to thaw.

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Surprisingly, the bipolar separator plate of the present invention, with a water absorption of 18 wt%, showed no cracking after undergoing 12 freeze / thaw cycles.

The separator plate 39 according to the present invention uses a wetting agent that is uniformly distributed in the separator plate and can still maintain sufficient electronic conductivity. According to a preferred embodiment, the wetting agent is added as a fine powder to the mixture of the electronically conductive material and the resin and is intimately mixed with them, obtaining a homogeneous distribution of the wetting agent. However, it can also be added as a mixed solution which, when thoroughly mixed with the electronically conductive material and resin, produces an extrudate material that is also uniformly mixed. The wetting agent promotes the formation of pores in the extruded material, thereby preventing the resin and other components from forming a continuous phase. The affinity of these wetting agents for water reduces the surface tension between the water and the extruded product. As a result, water in contact with the embossed plate forms a glutinous film on the surface of the embossed plate rather than drops. Since the embossed board may contain pores, they will be more easily filled with water due to the hydrophilic nature of the board. If sufficient differential pressure is applied across the plate, water can be transferred from one face of the plate to the other face of the plate. Another result obtained by a separator plate according to the present invention is the stability of the plate. We have found that the panel of the present invention retains 99% of its original weight after more than 1200 hours in water at 90 ° C. During this time, the water absorption in the slab also remained constant at 18 weight percent.

The conductivity of the separator plate according to the present invention as a function of the silica content is shown in Fig. 2 where several plates were made with different silica content evenly distributed in the plates. The separator plates from which this data is obtained contain a thermosetting resin in an amount of about 12.5% by weight of the separator plate, silica in an amount between 0% and 10% by weight of the separator plate, and graphite in an amount between 77.5% and 87.5% by weight separator plates.

Separator plates 39 suitable for use in proton exchange membrane fuel cells should have an electrical conductivity of not less than about 5 S / cm, and preferably not less than about 75 S / cm. The separator plates 39 of the present invention may be porous or non-porous, but must in any case be gas impermeable. According to a particularly preferred embodiment of the present invention, the plates are porous, have a porosity of less than about 25% by volume. The pore diameters of the separator plate 39 of the present invention are preferably in the range from about 0.25 microns to about 2 microns; wherein the average pore diameter preferably ranges from about 0.5 micron to about 1.5 micron.

In addition to the hydrophilic agent, the separator plate of the present invention comprises at least one electronically conductive material and at least one resin, wherein the electronically conductive material is present in amounts of from about 50% to about 95% by weight of the separator plate 39, and at least one resin is present in amounts. at least 5% by weight of the separator plate. Suitable electronically conductive materials for use in the separator plate of the present invention are selected from the group consisting of carbon-containing materials, metals, metal alloys, metal carbides, metal nitrides, and mixtures thereof. Suitable metals are titanium, niobium, tantalum, and alloys such as those of the Ni-Mo-Fe group.

According to a particularly preferred embodiment of the present invention, the electronically conductive material is a carbon containing material selected from the group consisting of graphite, carbon black, carbon fibers, and mixtures thereof. Graphite or various electrically conductive carbon compounds available, such as electrically conductive carbon black, are particularly preferred. The use of carbon-based materials reduces manufacturing costs as well as simplifying the fabrication of gas flow control means such as plate channels and plate extrusion.

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According to a preferred embodiment of the present invention, the separator plate 39 comprises up to about 10% by weight of carbon fibers. The addition of carbon fibers not only strengthens the board, but also supports the water absorption and conductivity of the board.

The separator plate of the present invention also contains greater than about 5% resin. The resin acts as a binder for the pressed-in separator plate 39 and, as already mentioned, can also increase the water absorption of the plate. Suitable resins are thermosetting resins, thermoplastic resins, and mixtures thereof. Suitable thermoplastic resins for use in the separator plate 39 of the present invention are polyvinylidene fluorides, polycarbonates, nylons, polytetrafluoroethylenes, polyurethanes, polyesters, polypropylenes and HDPE. Preferred thermosetting resins are selected from the group consisting of phenolic resins, aldehydes, epoxy and vinyl resins.

The following examples show the relationship between the various compositions of the separator plate according to the present invention and the properties of the obtained separator plate. In each case, porous separator plates measuring 10.2 by 10.2 cm were extruded from various mixtures of Varcum 29338 phenolic resin, having particle sizes less than 200 sieve units, obtained from Occidental Chemical Corporation of Dallas, Texas, silica particles with dimensions of 40 nanometers, carbon fibers having a length of about 150 microns, and graphite powder having a particle size less than 200 sieve units. The powders were carefully mixed and a plate was pressed from them at a pressure of 6900 kPa and a temperature of 204 ° C. Examples I to IV show the effect of silica on the conductivity and water absorption of the separator plates at room temperature. Conductivity and water absorption as a function of silica content are also shown in Figures 2 and 3, respectively. Example 5 shows the properties of a separator plate 39 according to one embodiment of the present invention having 10 weight percent graphite replaced by carbon fibers. Based on the results of Examples I to IV, it can be seen that when silica is added to the mixture, the water absorption of the plates, indicated by the amount of water absorbed, increases while the electrical conductivity of the plate decreases. However, by using 10 percent by weight of carbon fibers in place of the electronically conductive graphite material used in the mixture, the porosity of the board increases, the amount of wetting agent (silica) needed to achieve significant water absorption (18%) is reduced, and the conductivity of the board with a reduced silica content is higher than that of the boards. containing an appropriate amount of silica and devoid of carbon fibers (Example 2).

Example I

The plate was pressed at a pressure of 6900 kPa at 204 ° C with the following composition and properties:

Composition Type Percentage by weight Phenolic resin Varcum 2938 12.5 Silica * Aerosil OX-50 0.0 Graphite ** HPS-75 87.5 Properties Conductivity (S / cm) 130.0 Absorbed water (% wt) 5.6

* Degussa Corp. Of Richfield Park, New York ** Dixon-Ticonderoga Company of Lake Hurst, New Jersey

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Example II

The plate was pressed at a pressure of 6900 kPa at 204 ° C with the following composition and properties:

Composition ^T yp Percentage by weight Phenolic resin Varcum2938 12.5 Silica Aerosil OX-50 2.5 Graphite HPS-75 85.0 Properties Conductivity (S / cm) 90.0 Absorbed water (% wt) 5.9

Example III

The board was pressed under a pressure of 6900 kPa at 204 ° C with the following composition and properties:

Composition Type Percentage by weight Phenolic resin Varcum 2938 12.5 Silica Aerosil OX-50 5.0 Graphite HPS-75 82.5 Properties Conductivity (S / cm) 74.0 Absorbed water (% wt) 6.7

Example IV

The board was pressed under a pressure of 6900 kPa at 204 ° C with the following composition and properties:

Composition Type Percentage by weight Phenolic resin Varcum 2938 12.5 Silica Aerosil OX-50 10.0 Graphite HPS-75 77.5 Properties Conductivity (S / cm) 53.0 Absorbed water (% wt) 8.2

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Example V

The board was pressed under a pressure of 6900 kPa at 204 ° C with the following composition and properties:

Composition Type Percentage by weight Phenolic resin Varcum 2938 12.5 Silica Aerosil OX-50 2.5 Graphite HPS-75 75.0 Carbon fiber * Panex 30 10.0 Properties Conductivity (S / cm) 95.0 Absorbed water (% wt) 18.0 Medium pore size (MPS) 0.5 p

* Yolk Corporation from St. Louis, Missouri

Flexibility is the ability of the body to recover size and shape after deformation, caused, for example, by compressive stress. The flexibility of the graphite used in the separator plate of the present invention is approximately 26%. That is, when a compressive stress is applied, the graphite expands to about 126% of the compressed shape. In contrast, carbon fiber has much more flexibility. A separator plate having a higher flexibility due to the flexibility of the individual components making up the separator plate is undesirable as it limits the pore size that can be obtained. In particular, the use of materials having greater flexibility results in a board with larger pore sizes, and the use of materials with less flexibility results in a board with smaller pore sizes. Larger pore sizes generally reduce the pressure required for the reaction gases to pass from one side of the separator plate to the other and reduce the conductivity of the plate. Plates that use materials with low elasticity are generally stronger and conduct electricity better. The mixture of graphite and carbon fibers as used in Example 5 gives a board with a flexibility corresponding to that of graphite alone. This is surprising as one skilled in the art would expect that the addition of carbon fibers, which have a much higher flexibility than graphite, would result in a board with much higher flexibility. Thus, according to a particularly preferred embodiment of the present invention, the amount of carbon fibers present in the separator plate of the present invention is less than about 10% by weight.

The bubble pressure of the separator plate relates to its ability to prevent reaction gases from permeating from one side of the separator plate to the other. The bubble pressure is the positive pressure of the water in the pores of the separator plate, which is inversely proportional to the pore size of the plate. In other words, the smaller the average pore size, the greater the pressure exerted by the water absorbed in the plate. The bubble pressure is thus the pressure above which the reaction gases will be passed through the water-saturated plate, causing undesirable mixing of the two reactants as well as entering the reaction gases into the cooling water channels of the separator plates. We have found that the separator plates of the present invention have a bubble pressure greater than 34.5 kPa. Preferred embodiments of the separator plate of the present invention have an bubble pressure greater than 69 kPa, and more preferably greater than 138 kPa.

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As can be seen from the examples, there is a balance that must be achieved in the composition of the separator plate in order to obtain a plate having the desired conductivity and water absorption. The examples show that when the amount of SiO ₂ wetting agent is increased to increase the water absorption, the conductivity of the board decreases. Fig. 3 shows the increase in the amount of absorbed water in the slab with increasing SiO ₂ content, and Fig. 2 shows the decrease in conductivity with increasing SiO ₂ content. The graphs intersect for a silica content of about 5% by weight. Accordingly, the preferred ranges of silica used in the separator plate of the present invention are from 1 to 10% by weight, most preferably from 2% to 4% by weight. The addition of carbon fibers, as previously mentioned, up to 20% by weight, provides additional porosity without losing conductivity. However, carbon fibers are expensive and, therefore, it is desirable to minimize the amount used.

The separator plate 39 of the present invention is suitable for use in either an external fuel supply fuel cell stack or an internal fuel supply fuel cell stack. In the case of an external fuel supply fuel cell stack, the reaction gases are supplied from an external conduit system ^ connected to the extreme areas of the fuel cell stack, while in the case of an internal fuel supply fuel cell stack, the reaction gases are supplied by a distributor formed by perforations in cell components to reaction sites. A fuel cell stack with internal fuel distribution employing bipolar separator plates according to one embodiment of the present invention is shown in Fig. 4. As can be seen in Fig. 4, the ion exchange membrane 25 and the separator plate 39 of the fuel cell stack extend to the edge of the stack. The separator plates 39 are provided with flat peripheral sealing structures 43, extending from each face to contact with the ion exchange membranes 25 around their entire periphery, thereby forming an edge seal. The ion exchange membranes 25 and the separator plates 39 are formed with a plurality of fuel gas distribution holes 54, one for supply and one for evacuation, and a plurality of oxidant distribution openings 55, one for supply and one for removal of oxidant. The distribution openings 54,55 in the separator plate 39 are surrounded by flat gaskets 56,57 constituting the distributor seal, extending from each surface of the separator plate 39 to contact with the ion exchange membrane 25, thereby sealing the distributor and thereby forming a seal. numerous fuel and oxidant gas distributors that extend through the stack of cells. Gaseous fuel flow conduits 47, 47 'are formed in the planar sealing structures 56,57 of the separator plate 39 surrounding the fuel distribution openings 54 of the separator plate 39 on the surface facing the anode 30, so as to allow the gas fuel to flow between one set of distributors and the anodic reaction regions. between the anodes 30 and the surfaces of the separator plates 39 facing the anode 30, and the planar sealing structures 57 of the separator plates 39 are formed with oxidant gas flow conduits 48 and 48 'surrounding the oxidant distribution openings 55 on the surface of the separator plate 39 facing the anode 30. cathode 35, allowing the oxidant gas to flow between the second set of distribution channels and the cathode chambers formed between the cathodes 35 and the cathode faces 35 of the separator plates 39, thus ensuring full internal distribution of fuel gas and oxidant gas to and from each of each fuel cell in the fuel cell stack.

The bipolar separator plates 39 in this embodiment are produced by mixing at least one electronically conductive, preferably carbon containing, material, at least one resin and at least one hydrophytic agent, so as to form a substantially homogeneous mixture containing about 50% to 95% by weight of said conductive material. electronically material, at least about 5% by weight of said resin and said wetlanding agent. The mixture is then extruded into the desired shape at a temperature ranging from about 121 ° C to about 260 ° C and a pressure ranging from about 3447 kPa to about 27579 kPa.

189 780

According to one embodiment of the present invention, in the PEM fuel cell stack, the separator plate 39 of the present invention includes water supply and removal means to circulate and remove cooling water from the interior of the fuel cell stack. As can be seen in Fig. 1b, the separator plate 39, including the plate 39a facing the cathode and the plate 39b facing the anode, has a plurality of cooling water channels 34 therebetween. In a fuel cell stack with internal fuel distribution, as shown in Fig. 4, water is supplied from the water distribution openings 58, which are provided with expanded seals to seal against adjacent cell components and that form water flow lines between the water distribution openings 58 and through cooling water channels 34 having a water outlet 58 'in the separator plate 39.

FIG. Ib

189 780

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u_ [lM0 / S] OSONOOM32Hd

189 780

189 780

FIG. 4

189 780

FIG. la

Publishing Department of the UP RP. Circulation of 50 copies

Price PLN 4.00.

Claims (32)

Patent claims A bipolar separator plate for a proton exchange membrane fuel cell stack, comprising at least one electronically conductive material, at least one resin and at least one hydrophilic agent attracting water to the separator plate of a proton exchange membrane fuel cell stack, characterized in that each the at least one electronically conductive material is a carbon containing material and the material is from 50% to about 95% by weight of the separator plate, at least one resin is a phenolic resin in an amount of at least 5% by weight of the separator plate, and the hydrophilic agent is the silica contained in the separator plate. from 0.01% to 5% by weight of the separator plate, and the separator plate comprises a maximum amount of carbon fibers of up to 45% by weight of the separator plate, at least one electronically conductive material, at least one resin, at least one hydrophilic agent, and the carbon fibers are spaced reasonably evenly ernie. 2. The plate according to claim The resin of claim 1, wherein the at least one resin is hydrophilic. 3. The plate according to claim The method of claim 1, wherein the hydrophilic agent is a wetting agent. 4. The board according to p. The method of claim 5, wherein the wetting agent comprises a mixture of silica and metal oxides selected from the group consisting of Ti, Al. 5. The board according to p. The method of claim 1, wherein the at least one phenolic resin is selected from the group consisting of thermosetting resins, thermoplastic resins, and mixtures thereof. 6. The board according to p. The method of claim 1, wherein the at least one carbon-containing electronically conducting material is selected from the group consisting of graphite, carbon blacks, carbon fibers, and mixtures thereof. 7. The board according to p. The composition of claim 1, which is porous. 8. The board according to p. 9. The separator plate as claimed in claim 9, wherein the porosity of the separator plate is less than 5% by volume of the plate. 9. The board according to p. The pharmaceutical composition of claim 7, wherein the pores have an average diameter ranging from 0.25 microns to about 2.0 microns. 10. The board according to claim 10. The plate of claim 10, wherein the bubble pressure is greater than 34.5 kPa. 11. The board according to p. The separator plate of claim 1, wherein the specific conductivity of the separator plate is at least 5 S / cm. 12. The board according to p. The composition of claim 1, wherein the electronically conductive material comprises 70% to 90% by weight, 8% to 15% by weight of thermosetting phenolic resin, up to 10% by weight of carbon fibers, and 0.01% to 5.0% by weight. silica. 13. The board according to claim A device according to claim 1, characterized in that between its surface (31) facing the anode (30) and its surface (36) facing the cathode (35) there are means for circulating water. 14. A method for producing a bipolar separator plate for a fuel cell stack, wherein mixing at least one electronically conductive material, at least one resin, at least one hydrophilic agent selected for a fuel cell with a proton exchange membrane, and then forming the plates with the required shape, characterized in that the electronically conductive material is a carbon-containing material in an amount of 50% to 95% by weight of the mixture, a phenolic resin is used as the resin in an amount of at least 5% by weight of the mixture, and the hydrophilic agent is 189 780 silica in an amount of 0.01 to 5% by weight of the mixture and carbon fibers are added in a maximum amount of up to 45% by weight, and these components of the mixture are mixed until a homogeneous mixture is obtained, and then a separator plate of the required shape is formed at a temperature from 121 ° C to 260 ° C and pressures ranging from 3447 kPa to 27579 kPa. 15. The method according to p. The process of claim 14, wherein the resin is a hydrophytic resin. 16. The method according to p. The process of claim 14, wherein the hydrophilic agent is a wetting agent. 17. The method according to p. The process of claim 14, wherein the hydrophilic agent is a mixture of silica and a metal oxide selected from the group consisting of Ti, Al. 18. The method according to p. The process of claim 14, wherein the phenolic resin is selected from the group consisting of thermosetting resins, thermoplastic resins, and mixtures thereof. 19. The method according to p. The process of claim 14, wherein the carbon-containing material is selected from the group consisting of graphite, carbon black, carbon fibers, and mixtures thereof. 20. A fuel cell stack comprising a plurality of individual fuel cells each containing an anode, a cathode, an ion exchange membrane disposed between the anode and cathode, and a separator plate having an anode-facing surface and a cathode-facing surface, the separator plate is interposed between the anode of one fuel cell and the cathode of an adjacent fuel cell and comprises at least one electronically conductive material, at least one resin and at least one hydrophilic agent, characterized in that the separator plate (39) comprises uniformly distributed therein at least one electronically conductive material containing carbon in an amount ranging from 50% to 95% by weight of the separator plate (39), at least one phenolic resin in an amount of at least 5% by weight of the separator plate (39), a silica hydrophilic agent in an amount from 0 .01% to 5% by weight of the separator plate, and also contains carbon fibers in a maximum amount of up to 45 % by weight of the separator plate (39) and the ion exchange membranes (25) and the separator plates (39) each extend to the edge of the fuel cell stack (15), the separator plate (39) having flat peripheral sealing structures (43). extending from each surface of the separator plate (39) to contact the ion exchange membranes (25) around their entire edge and forming an edge seal, and the ion exchange membrane (25) and the separator plate (39) have multiple fuel (54) and oxidant distribution holes (55) facing each other, the distribution openings (54, 55) of the separator plates (39) being surrounded by planar sealing structures (56, 57) extending from the surface of the separator plate (39) to contact the ion exchange membrane (25) and forming the gaseous fuel and oxidant distribution channels extending through the stack of cells, and in the planar sealing structures (56, 57) are formed flow conduits (47, 47 ') for the flow of gaseous fuel between one set of distribution channels and the anode chambers formed between the anodes (35) and the anode-facing surfaces of the separator plates (39), and there are formed oxidant gas flow conduits (48, 48 ') between the second set of distribution channels and the cathode chambers formed between the cathodes (35) and the surfaces of the separator plates (39) facing the cathodes (35). 21. The stack of claim 1 The process of claim 20, characterized in that the separator plate (39) comprises at least one hydrophilic resin. 22. The stack according to claim 22 The method of claim 20, characterized in that the hydrophilic agent of the separator plate (39) is wetting. 23. The stack of claim 1 The method of claim 22, characterized in that the hydrophilic wetting agent of the separator plate (39) comprises a mixture of silica and metal oxides selected from the group consisting of Ti, Al. 24. The stack according to claim 24 The method of claim 24, characterized in that the phenolic resin of the separator plate (39) is selected from a thermosetting resin, a thermoplastic resin, and mixtures thereof. 25. The stack of claim 1 The method of claim 20, wherein the carbon-containing electronically conducting material of the separator plates (39) is selected from the group consisting of graphite, carbon black, carbon fibers, and mixtures thereof. 189 780 26. The stack of claim 1 20, characterized in that the separator plate (39) comprises pores. 27. The stack of claim 1 The method of claim 26, characterized in that the porosity of the separator plate (39) is less than 25% by volume of the plate. 28. The stack of claim 1 The method of claim 27, characterized in that the pores of the separator plate (39) have an average diameter ranging from 0.25 microns to 2.0 microns · '. 29. The stack of claim 1 The method of claim 26, characterized in that the separator plate (39) has a bubble pressure greater than 34.5 kPa. 30. The stack of claim 1 The method of claim 20, wherein the separator plate (39) has a specific electrical conductivity of at least about 5 S / cm. 31. The stack of claim 1 20, characterized in that the gas flow conduits (47, 47 '; 48, 48') are formed in a central region of the separator plate (39). 32. The stack of claim 1 The method of claim 20, comprising water distribution holes (58) for circulating and removing water from the fuel cell stack.